1. Field of the Invention
The present invention relates to a system for measuring a surface profile of an object and, more particularly, a system for optically detecting a surface condition of an object without contacting the object.
2. Description of the Related Art
The surface roughness tester of the probe type is well known as a system for measuring the minute roughness of the surface of an object. However, this surface roughness tester cannot measure the surface deviation of high density LSIs (or DRAMs and the like) having trenches each 0.5-10 .mu.m wide and 1.0-20 .mu.m deep, since the tip end of the probe cannot be inserted into such trenches, and the probe may damage their surfaces. It is therefore supposed that this surface roughness tester cannot be used to measure such minute surface deviation.
Electron micrographs are used to examine the dimension and shape of the trenches of these high density LSIs, but the object to be measured may be broken to get these electron micrographs. This is not suitable for use as the manner of examining the minute roughness of object surfaces.
There has been proposed an optical system for measuring the minute roughness of the surface of the object without taching the object. In this optical system, a bundle of white light rays are radiated on an object to be measured, a bundle of light rays reflected from the object are separated into one component reflected from the reference surface of the object and the other component reflected from the bottom of a trench formed on the surface, and the depth of the trench is obtained from spectral interference signals of the both components. There has been also proposed an another optical system utilizing the Michelson interferometer for measuring a roughness of the surfaces of object without contacting the objects. In this another system, a bundle of while light rays is radiated onto an object to be measured, the reference mirror is scanned with a bundle of reference light rays and an interference of the both bundle of light rays is detected so that the depth of the trench can be obtained from intervals between three peaks of the interference.
According to these systems for optically measuring the minute roughness of surface, it is possible to obtain the mean value of depths of the trenches in a certain area. However, it is not possible to obtain the depth of each of trenches. In addition, they take several seconds for measuring the object.
In order to solve these problems, Mr. Hitoshi Takabayashi, inventor of the Laid Open Japanese Patent Application Sho 58-47209 (publicly opened on Mar. 18, 1983), had proposed an optical system, in which the surface of an object to be measured is traced with a convergent laser beam emerged from a projection lens, the laser beam reflected from the object surface to a photo detector. When the laser beam converged by the projection lens enters into a recess such as the trench in this system, it is reflected from the bottom of the trench at an angle different from the angle at which the laser beam is reflected from a reference surface, these laser beams transmitted through the image forming lens form their spots on the photo detector at different positions thereof and the depth of the trench is obtained from the distance between these laser beam spots.
In the above described system, when a high magnification lens is used to form a minimum spot on the object, it is impossible to obtain on proposed optical arrangement, because a working distance is shortened in accordance with the magnification of the lens. Thus, the beam spot size is limited from the working distance. Accordingly, and this system has a limitation in its measuring accuracy.